Given the current brouhaha in Congress over immigration reform, it’s easy to forget that on this day 58 years ago, Washingtonians were worried about illegal aliens of a different sort. This declassified Air Force reportdescribes the sighting of a UFO hovering over the Pentagon on the evening of July 27, 1952. The witness, a woman from Arlington, VA, reportedly observed a bright white light that lingered over the Department of Defense, made a descent toward it, and then abruptly took off. It actually was the second UFO sighting of the evening — the same object, or a similar one, reportedly appeared over the U.S. capitol at about 7:30 p.m., according to a chronology of sightingscompiled by the National Investigations Committee on Aerial Phenomena, a private-sector UFOlogy group. It was never determined whether the sighting was actually a spacecraft, or merely an illusion caused by random emissions of swamp gas from a Congressional debate. But while you’re waiting for the Men in Black to show up and erase your memory of reading this article, here are the science stories of the day.

Did a comet cause the Ice Age, or not?Some scientists think the great Ice Age 10,000 to 12,000 years ago was triggered by pollution from fires caused by a comet collision with Earth. But others say, uh-uh.